The silver halides employed in silver halide photographic photosensitive materials are generally chemically sensitized to obtain a desired photographic speed and gradation, etc.
Known chemical sensitization methods include sulfur sensitization using active gelatin or compounds which contain sulfur that reacts with silver ions, selenium sensitization using selenium compounds, reduction sensitization using reducing substances and precious metal sensitization using gold or other precious metal compounds. These methods may be employed either individually or in combination.
Thiosulfate, thioureas, thiazoles, rhodanines and other compounds can be used as sulfur sensitizing agents; selenoureas and colloidal Se, for example, can be used as selenium sensitizing agents; stannous salts, amines, hydrazine derivatives, formamidinesulfinic acid and silane compounds, for example, can be used as reduction sensitizing agents; and, as complex salts of metals of group VIII of the periodic table ("the periodic table" based on herein is "PERIODIC CHART OF THE ELEMENTS" in The Merck Index, inside front cover, published by Merck & Co., Inc., 1989), such as platinum, iridium and palladium, for example, as well as gold complex salts, can be used for precious metal sensitization purposes.
Reference can be made, for example, to Research Disclosure volume 307, page 866 (1989) for actual examples of these chemical sensitizing agents, and they are well known to those in the industry.
Moreover, chemical sensitization promoters are used conjointly with the addition of these well known chemical sensitizing agents to inhibit fogging and increase photographic speed. Specific examples of such promoters which can be used include: compounds which are referred to as silver halide solvents, such as thiocyanate (for example, potassium thiocyanate, ammonium thiocyanate); thioether compounds (for example, the compounds disclosed in U.S. Pat. Nos. 3,021,215 and 4,276,374) and thione compounds (for example, the compounds disclosed in JP-B-59-11892, JP-B-60-11341 and U.S. Pat. No. 4,221,863); adsorbable compounds which can bond with silver ions at a nitrogen atom and form complex salts such as the azaindenes (for example, 4-hydroxy-6-methyl-1,3, 3a,7-tetraazaindene), azapyridazines, azapyrimidines and purines (for example, adenine) disclosed in the aforementioned Research Disclosure volume 307, page 866 (1989); and, the adsorbable compounds in which a mercapto group that bonds with silver ions is substituted in a heterocyclic ring, such as the mercaptoazoles, typified by the mercaptotetrazoles and mercaptotriazoles disclosed in Research Disclosure volume 307, page 869 (1989). (The term "JP-B" as used herein signifies an "examined Japanese patent publication".)
However, these chemical sensitization promoters are often cause various adverse effects. Thus, when a silver halide solvent is used, and especially when it is used in large amounts, a high photographic speed and reduced fogging are certainly obtained immediately after the completion of chemical sensitization; but, there is a pronounced decrease in the photographic speed on ageing, and the level of fogging increases. This deterioration in performance is especially pronounced when sensitizing dyes are also present.
Furthermore, the use of adsorbable compounds can result in pronounced inhibition of the adsorption of sensitizing dyes.
The presence of these chemical sensitization promoters is necessary during chemical sensitization, but their presence results in adverse effects if they remain in the silver halide emulsion after the completion of chemical sensitization, and these effects are especially pronounced when color sensitization is carried out.
Hence, the development of a method of inhibiting the action of these chemical sensitization promoters after the completion of chemical sensitization is desirable.